Langley's chief scientific interest was
the sun and its effect on the
weather, and believed that all life and activity on the Earth were made
possible by the sun's radiation. In 1878 he invented the bolometer, a
radiant-heat detector that is sensitive to differences in temperature of
one hundred-thousandth of a degree Celsius (0.00001 C) . Composed of
two thin strips of metal, a Wheatstone bridge, a battery, and a
galvanometer (an electrical current measuring device), this instrument
enabled him to study solar irradiance (light rays from the sun) far into
its infrared region and to measure the intensity of solar radiation at
various wavelengths.

Bolometers
have been flown on numerous NASA
missions including the Earth's Radiation Budget Experiment (ERBE) and the
Clouds and Earth's Radiant Energy System (CERES), which
provided accurate regional and global measurements of the components of
the Earth's radiation budget. Langley's highly original and innovative
research earned him honorary doctorates, awards, and medals from
universities and scientific societies around the world.